Instability of the microtubules of the connecting cilia has been suggested as a cause or complicating factor in some cases of retinitis pigmentosa. These microtubules are normally highly acetylated on Lys40 of ` tubulin, a posttranslational modification that appears to be restricted to polymerized microtubules; the function of this acetylation is as yet unknown. We have described the case of an infertile male subject with a rod-dominant retinal degeneration whose sperm flagella show severe morphological abnormalities and greatly reduced acetylation. Currently, the project is directed toward characterization of tubulin acetyl transferase (TAT) using bovine retina an brain as the source. TAT has been purified about 1,000-fold and is in a complex of about 300 kDa. SDS-PAGE analysis of the complex shows four major and several minor bands ranging from 30 to 120 kDa. The major bands are N-terminal blocked and will require digestion and purification of peptides before sequencing can be done. Arrestin (S-antigen) copurifies with the TAT complex from retina and is a substrate for the acetyltransferase activity. A 70 kDa band of gamma-immunoreactive material is also found in the TAT complex from both brain and retina. The partially purified TAT complex from Y-79 retinoblastoma cells is under evaluation for use in future studies of the molecular biology of the TAT complex.